Research team

Nanostructured and organic optical and electronic materials (NANOrOPT)

Expertise

- Characterisation of paramagnetic inorganic and organic compounds - Characterisation of paramagnetic impurities and defects in solids. - Optical characterisation (absorption, fluorescence, raman spectroscopy) of liquids and solids. - Optical investigations of ultrafast dynamics in materials - Determination of nonlinear optical (NLO) properties of molecules in solution.

TunabLe pulsed And continuouS-wavE laseR facility (T-LASER). 01/01/2020 - 31/12/2021

Abstract

T-LASER comprises the extension of a laser facility to a versatile wavelength-tunable pulsed and continuous-wave (CW) laser platform operating from the ultraviolet to the infrared range of the optical spectrum, for enabling a wide range of advanced spectroscopic techniques and laser-based applications – the key research capabilities of the ECM group. Thanks to a large fraction (78%) of co-funding, a laser platform will be built that is not only essential to all of ECM's ongoing research projects and its many collaborations, but actually establishes a world-wide unique laser facility. Moreover, this central laser platform will be complemented with a range of optical satellite setups that are already available (and already unique) and will be further developed. The versatility of the laser facility, both in pulse duration and wavelength tunability, will enable unprecedented optical experiments, such as widely continuously tunable resonance Raman scattering, and nonlinear optical scattering such as widely wavelength-tunable (second- and third-order) hyper-Rayleigh and hyper-Raman scattering. This will form a highly complementary set of unique techniques, making UAntwerp an extremely desirable partner for research groups active in the involved technologies, worldwide.

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Electrical and physical characterization of trap states at the SiC/gate dielectric interface in SiC metal-oxide-semiconductor field-effect transistors. 01/04/2019 - 31/03/2023

Abstract

This is a research project financed by the Vlaio agency for innovation and entrepreneurship (VLAIO - Vlaanderen). The project was subsidized after selection by the expert panel. The project is conducting in collaboration with Flemish Industry.

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Spectroscopic identification of defects in materials for perovskite-based hybrid solar cells. 01/10/2018 - 30/09/2020

Abstract

Organometal trihalide perovskite solar cells have in the few years since their first introduction (in 2009) demonstrated very high power conversion efficiencies, up to 21% with potential for further increase. It is announced to become a game changer in the field of thin film photovoltaics, but this will critically depend on avoiding defect formation in the perovskite layer as well as at the interfaces with adjacent layers. The defects act as trapping centers for negative and positive charge carriers and as such impede the carriers to contribute to the photocurrent. The defects may result from the material synthesis and device fabrication methods, but they can also appear due to degradation, thereby reducing the useful lifetime of the solar cells. The main goal of my project is the identification and characterization of the defects that set a limitation to the solar cell performance. To learn about the geometric and electronic structure of these defects I will apply multi-frequency electron paramagnetic resonance (EPR) techniques which are able to reveal the nature of the defects and of their surroundings. Knowledge of the electronic structure and creation processes of the defects will allow to design better perovskite materials for these solar cells and to optimize the device fabrication process.

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Design of generic assays based on electron paramagnetic resonance to understand degradation processes in novel fullerene-free organic solar cells. 01/01/2017 - 31/12/2020

Abstract

The constantly increasing global energy demand and massive use of fossil fuels is putting a very heavy burden on our environment. Not surprisingly, policy makers world-wide are pressing for renewable and eco-friendly alternative energy sources. Solar energy is inexhaustible and offers many possibilities. In principle, organic solar cells (OSCs) would be ideal, since they are light, flexible, and offer the potential of large-area fabrication. Their cost can be kept low, provided nonfullerene OSCs with sufficient power conversion efficiencies can be found. The recent successes in synthesis of materials for non-fullerene OSCs are very promising. However, one of the biggest problems common to all OSCs is the poor stability of the cells. Advancements in OSC stability can only be obtained through in-depth knowledge of the molecular reaction paths and morphological changes that impair this stability. This in turn requires good assays to monitor and evaluate these processes. This project targets at the development of a systematic methodology, based on different electron paramagnetic resonance techniques, to study mechanistic steps in OSC degradation on a molecular level. The assays will be optimized for studies of both the organic core materials (blends) and the corresponding OSC devices. The methodology will be applied here to the case of non-fullerene OSCs, but will be generic for studies of other OSCs and related novel photovoltaic devices.

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Spectroscopic identification of defects in materials for perovskitebased hybrid solar cells. 01/10/2016 - 30/09/2018

Abstract

Organometal trihalide perovskite solar cells have in the few years since their first introduction (in 2009) demonstrated very high power conversion efficiencies, up to 21% with potential for further increase. It is announced to become a game changer in the field of thin film photovoltaics, but this will critically depend on avoiding defect formation in the perovskite layer as well as at the interfaces with adjacent layers. The defects act as trapping centers for negative and positive charge carriers and as such impede the carriers to contribute to the photocurrent. The defects may result from the material synthesis and device fabrication methods, but they can also appear due to degradation, thereby reducing the useful lifetime of the solar cells. The main goal of my project is the identification and characterization of the defects that set a limitation to the solar cell performance. To learn about the geometric and electronic structure of these defects I will apply multi-frequency electron paramagnetic resonance (EPR) techniques which are able to reveal the nature of the defects and of their surroundings. Knowledge of the electronic structure and creation processes of the defects will allow to design better perovskite materials for these solar cells and to optimize the device fabrication process.

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Spectroscopic identification of charge carriers and defects in materials for perovskite-based hybrid solar cells. 01/10/2015 - 30/09/2016

Abstract

Organometal trihalide perovskite solar cells have in the few years since their first introduction (in 2009) demonstrated very high power conversion efficiencies, up to 18% with potential for further increase. It is announced to become a game changer in the field of thin film photovoltaics, but this will critically depend on avoiding defect formation in the perovskite layer as well as at the interfaces with adjacent layers. The defects act as trapping centers for negative and positive charge carriers and as such impede the carriers to contribute to the photocurrent. The defects may result from the material synthesis and device fabrication methods, but they can also increasingly appear due to degradation, thus reducing the useful lifetime of the solar cells. The main goal of my project is the identification of the defects that either set an initial limitation to the solar cell performance or else cause degradation of the solar cell during operation. To learn about the geometric and electronic structure of these defects I will apply multi-frequency electron paramagnetic resonance (EPR) techniques which are able to reveal the nature of the defects. Knowledge of the electronic structure and creation processes of the defects will allow designing better perovskite materials for these solar cells and to optimize the device fabrication.

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AGRECHEM: Antwerp Green Chemistry. 01/01/2015 - 31/12/2019

Abstract

This project represents a research contract awarded by the University of Antwerp. The supervisor provides the Antwerp University research mentioned in the title of the project under the conditions stipulated by the university. The AGRECHEM consortium is an excellence centre of the University of Antwerp, focusing on green and sustainable chemistry. One of the biggest future challenges is the production of fine chemicals in a sustainable way. The quest for synthetic routes that are at the same time eco-friendly and economically feasible requires a concerted input of scientists with a variety of specializations. The progress in synthesis goes hand in hand with progress in materials characterization. Therefore, the consortium brings together two main research groups on synthetic chemistry and three research units specialized in material characterization techniques with emphasis on gaining mechanistic insight in chemical reactions. The consortium aims at consolidating and increasing the existing excellence in sustainable chemistry at the University of Antwerp.

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Fullerene-free solution-processed bulk heterojunction organic photovoltaics. 01/01/2015 - 31/12/2018

Abstract

The general objective of this project is to improve organic solar cell performance on the basis of a more detailed fundamental understanding of the underlying properties and processes - such as electronic structure, charge transfer and transport, loss processes and bulk heterojunction blend morphology development - taking advantage of chemical engineering of non-fullerene electron acceptor materials (with all their possible advantages and hurdles to overcome).

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Correlation between structural and magnetic properties in chemically disordered FePt thin films 15/07/2014 - 30/04/2015

Abstract

The main objective of this project is to understand the correlation between the magnetic configuration of chemically disordered FePt thin films and the structural properties. The domain structure of FePt films depends strongly on the out of plane anisotropy (Kperp), film thickness, exchange constant and the saturation magnetization (Ms). Below a critical thickness (depending on the growing conditions) planar magnetic domains are found, while for larger thickness a stripe‐like magnetic structure forms. In order to obtain a phase diagram in critical thickness vs. the quality factor Q= Kperp/2Ms**2, we have grown a series of fifteen samples varying the film thickness and the Ar pressure in the sputtering chamber from 5 to 9 mTorr. By this procedure it is possible to maintain an almost constant crystalline texture, but relaxing the in‐plane stress. Previous measurements showed that stress is the predominant contribution in the perpendicular anisotropy. With an AFM‐MFM microscope, we have observed the transition from a striped pattern to in‐plane magnetic domains and we have also combined the image information with dc magnetization and ferromagnetic resonance (FMR) measurements at different microwave frequencies. We have already characterized the dynamical properties of FePt films in a limited set of samples obtaining the damping parameter from FMR linewidths as a function of excitation frequency. Extending these measurements to the new set of samples will allow us to examine a dependence of damping with the fabrication conditions. FMR measurements at high frequencies (W‐band, f=95GHz) are extremely useful for the precise determination of the damping parameter.

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Nanodiamond labelling of neuronal cells for molecular resolution neuronal and network-level imaging 01/07/2012 - 30/06/2016

Abstract

This interdisciplinary project addresses the interactions of functionalised nanoparticles with neural tissues and their usage to probe the local environment and neural function. Fundamental progress must be made in two main research areas, the design of nanodiamond particles and the understanding of their chemical, electronic, and optical properties, as well as the biological and biophysics aspects, in particular insertion of the nanoprobes, their biocompatibility and non-contact detection. In parallel with the materials research, explored thanks to a recently granted FWO-project, and in a highly independent and complementary approach, the present request for a doctoral research project will focus on the bio-related aspects and the detection at the molecular and cellular level. The uptake and anchoring of functionalised nanodiamond labels will be investigated and monitored by electrophysiological techniques and confocal microscopy, keeping track of the influence on neural function. Neuronal cell culture with nanodiamond loading will be optimized as well as the use of drugs that affect neural interconnection. This work in the Neurobiology laboratory will be combined with the assessment and optimisation of the advanced detection techniques developed in the Physics research group. Foerster resonance energy transfer (FRET) and optically detected magnetic resonance (ODMR) will be applied and optimised for neural cell investigation in a confocal microscopy configuration and compared to the more classical patch-clamp methods for the high temporal-resolution detection of neural electrical activity.

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Imaging neural activity at the cellular- and network-levels by optically detected diamond spin-magnetometers and nanoparticle FRET sensors. 01/01/2012 - 31/12/2015

Abstract

The project develops novel cellular imaging technique derived from optically detected magnetic resonance (ODMR) and Foerster Resonance Energy Transfer (FRET), manipulating single-photons and spins in nano-diamond (ND) particles. This original technique is proposed as a sound alternative to calcium- or voltage-sensitive fluorophores in front-edge neuroscience research. In our proposal we use ND particles that are engineered to contain Nitrogen-Vacancies (NV)-defect centers, used for quantum- optical and electrical imaging. Upon "transfection" of the neurons by functionalized NDs, this technique will enable us to investigate with optical signals and ultra-weak electromagnetic fields in single neurons and microcircuits, related to action- and synaptic potentials but currently fully unexplored. A novel "magnetic" description of neuronal excitability will then be addressed for the first time, based on extreme sensitivities to ultra-week magnetic fields when working with single spins.

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SILASOL - New Silicon Materials for Solar Applications. 01/01/2010 - 31/12/2013

Abstract

Silicon solar cells are the work horse of the photovoltaic energy conversion from sunlight into electricity.The SILASOL project focuses on new silicon-based materials for PV applications: by changing the shape of the silicon material (thinner wafers, nanowires, ...), or the synthesis method (CVD, mechanical cleavage, ...), the "new" Si material acquires specific properties (bandgap, crystallinity, ...) that can be used advantageously for PV applications. The technology development is in Imec (Leuven), the task of the UA is the experimental and computational characterization of these advanced silicon nanostructures.

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Charge transfer in semiconducting polymer / CVD diamond heterostructures. 01/01/2010 - 31/12/2013

Abstract

The general objective of this project is the study of the formation and the characterisation of organic materials/diamond heterostructures. Besides the fundamental interest in investigating different aspects of this new class of material systems, such structures can play an important role in future photovoltaic applications, photoelectrochemistry, etc. The key issues of the project are the deposition of new conjugated polymers and short change organic molecules, tailored for attachment to differently terminated diamond surfaces, the physical and chemical bonding between these two materials, and the examination of the possible charge-transfer mechanisms that will occur.

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Inter-university Research Center for Multi-frequency pulsed Electron paramagnetic resonance spectroscopy. 19/12/2008 - 18/12/2013

Abstract

This project represents a research contract awarded by the University of Antwerp. The supervisor provides the Antwerp University research mentioned in the title of the project under the conditions stipulated by the university.

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One-photon light sources based on doped diamond nanocrystals. 01/10/2008 - 30/06/2013

Abstract

Nitrogen and silicon associated vacancy defects in diamond are incorporated inside diamond nanocrystals for the production of single-photon light sources with promising perspectives for use in quantum cryptography and quantum computing. The dependence on production method and size of the nanocrystals will be studied, as well as the influence of irradiation and thermal posttreatments, in order to determine the optimal preparation routes.

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Determination and modeling of the dispersion of the molecular first hyperpolarisability: octupolar etallodendrimers and carbon nanotubes. 01/10/2008 - 30/09/2011

Abstract

The aim of this research project is to examine the dispersion of the molecular first hyperpolarisability ß, in order to develop a proper ß dispersion model. By performing wavelength-dependent HRS measurements onto a number of well-chosen model systems, the current models can be tested and improved, and if necessary a new approach can be developed.

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PolySpec - Nanostructured POLYmer phototvoltaic devices for efficient solar SPECtrum harvesting. 01/01/2008 - 31/12/2011

Abstract

The project aims at increasing the energy conversion efficiency of organic nanostructured bulk heterojunction photovoltaic devices as well as improving the stability of their nanomorphology. Progress on both fronts would allow envisaging outdoor large-scale application of these nanostructured PV-devices.

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The elucidation of complex electron paramagnetic resonance (EPR) spectra of novel stable radical cations - an interdisciplinary approach. 01/07/2007 - 30/06/2011

Abstract

Conjugated organic and organometallic compounds and their stable radicals, useful as organic semiconductors, will be synthesized and characterized using advanced pulse and multi-frequency EPR techniques. The combination with all-electron DFT quantum chemical calculations is essential to extract all available structural information contained in the spectroscopic data.

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    Microscopic structure and transformation processes of impurity defects in bismuth oxides: relation with photorefractive and scintillator properties of these materials. (FWO Vis.Fel., Vera GOSPODINOVA, Bulgaria) 01/04/2007 - 31/03/2008

    Abstract

    In doped bismuth-oxide crystals we will investigate the structure of impurity defects, as well as their transformations under optical and thermal treatments. This will be achieved by a combination of optical and EPR methods. The project will lead to a better understanding of the origin of the technologically important properties of these materials, and to new opportunities for their optimization.

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    Project website

    Boron-related centers in diamond in the cross-over region from p- to n-type conductivity: an investigation by electron paramagnetic resonance spectroscopy 01/02/2007 - 30/11/2007

    Abstract

    In boron doped diamond, the microscopic structure of B-related defects with acceptor or donor character will be investigated. EPR and ENDOR techniques will be applied to determine the defect symmetry and the interactions with neighboring nuclei. Measurements in the X-, Q- and W-band (9.4 GHz, 35 GHz and 94 GHz, resp.), including pulse EPR, will be performed for higher spectral resolution and selectivity.

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    Selective linear and nonlinear optical spectroscopy of carbon nanotubes and their interactions with organic molecules. 01/01/2007 - 31/12/2010

    Abstract

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    Interaction between conjugated molecules and single-walled carbon nanotubes. 01/01/2007 - 31/12/2008

    Abstract

    Carbon nanotubes (CNTs) are very interesting as one-dimensional systems with metallic or semiconducting properties. The conduction and mobility of holes and electrons can be described in the same way. It is also possible to dope these nanotubes by inserting small molecules in the CNTs. These doped CNTs are very stable by exposure to air and the choice of the inserted molecule controls the degree of doping. This project will deal with two different subjects. First we will study the charge transfer from the conjugated molecules to the SW CNTs. This charge transfer is of great importance for the use of such composites in plastic solar cells. Second, we will consider doping of the CNTs by inserting different conjugated molecules inside the CNTs. Both systems wil be studied by optical spectroscopy, pulsed laserspectroscopy and electron paramagnetic resonance (EPR).

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    Complex Spectroscopy of Defects Related to n-type Conductivity in Diamond: Microstructure and Kinetics. 01/01/2006 - 31/12/2007

    Abstract

    The goal of this project is to study the electronic properties, microstructure and migration of defects supplying efficient n-type conductivity in thin diamond layers, to investigate their migration and interaction with other defects under thermal and thermobaric treatments. We also include the study of n-type defects that are compensating the acceptors in electron irradiated boron-doped bulk diamond. Methods of optical (Raman scattering, photoluminescence, absorption), EPR (continuous-wave and pulse methods), and deep level transient spectroscopies will be used in conjunction with electrical measurements to characterize n-type defects in the samples synthesized in the NSC GPI team. The joint research of the teams from GPI and UA in the last few years concerning defects in diamond, offers a good basis for the successful realization of this project.

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    Investigation of structure and dynamics of surfactant layers around carbon nanotubes by means of spin-probe and spin-label EPR methods. (FWO Vis. Fel., Jelena CULIN) 01/11/2005 - 31/10/2006

    Abstract

    The spin-probe and spin-label methods in EPR will be applied to investigate the structure and dynamics of the contact regions between carbon nanotubes (CNTs) and conjugated polymers. For this purpose, advantage will be taken from the very efficient solubilization by bile salt surfactants. The micelles formed around the CNTs will also be studied by the spin-probe method.

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    Optical properties of nanostructured organic materials based on carbon nanotubes. 01/10/2005 - 30/09/2008

    Abstract

    The objectives of the study are: 1) To apply advanced optical techniques to the isolated CTN's in liquid and solid solution to get a better understanding of the electronic and optical properties of CNT's. 2) To develop a reliable characterization method using these optical techniques, for analyzing the composition of CNT materials. 3) To prepare composites of the individually dissolved CNT's with other molecules and polymers, and study the interactions occurring in these.

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    Interaction between conjugated molecules and single-walled carbon nanotubes. 01/01/2005 - 31/12/2006

    Abstract

    Carbon nanotubes (CNTs) are very interesting as one-dimensional systems with metallic or semiconducting properties. The conduction and mobility of holes and electrons can be described in the same way. It is also possible to dope these nanotubes by inserting small molecules in the CNTs. These doped CNTs are very stable by exposure to air and the choice of the inserted molecule controls the degree of doping. This project will deal with two different subjects. First we will study the charge transfer from the conjugated molecules to the SW CNTs. This charge transfer is of great importance for the use of such composites in plastic solar cells. Second, we will consider doping of the CNTs by inserting different conjugated molecules inside the CNTs. Both systems wil be studied by optical spectroscopy, pulsed laserspectroscopy and electron paramagnetic resonance (EPR).

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    Electronic structure, morphology and charge transfer in low-band gap polymers and polymer/carbon nanotubes hyrid films. 01/01/2004 - 31/12/2007

    Abstract

    De goal of this project is a fundamental investigation of a new class of conjugated polymers, called `low-bandgap polymers'. The essential targets can be summarized as follows: (1) Study of the electronic structure in low-bandgap polymers, in particular de band structure, the localized and excited states. To this end, further development of ultra-sensitive electro-optic characterization techniques, with the emphasis on photo-induced conductivity. (2) Investigation of transportmechanisms in these materials, such as the mobilities of the charge carriers and the factors by which they are determined. (3) Analysis of the mechanisms of charge carrier generation in these polymers and charge transfer in polymer mixtures and hybrid materials (polymer/fullerene or polymer/carbon nanotubes). (4) Study of the correlations between morfological and functional characteristics, which are partly determined by the forementioned properties.

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    Characterization of high-spin transition metal compounds by means of sophisticated EPR-techniques at high microwave frequency. 01/01/2004 - 31/12/2005

    Abstract

    By means of high frequency (95GHz) EPR-techniques specific families of organo metallic compounds can be studied. These systems have a high groundstate spin and can behave as single molecule magnets. The key to such behaviour is the zero-field splitting of the energy levels (=splitting of the energy levels in the abscence of a magnetic field). These zero-field splittings can be precisely analyzed using high frequent EPR techniques.

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    Nanosolar : Novel Nanostructured Hybrid Material Systems and Integration in Innovative Photovoltaic Concepts. 01/10/2003 - 30/11/2007

    Abstract

    The Nanosolar project aims to achieve a major step forward in the control of the morphology and functionality of organic based nanostructured hybrid material systems and their implementation in innovative photovoltaic devices. It is expected that resolving the issues encountered for photovoltaic devices will lead to a broad knowledge base, which encompasses fundamental insights in the relations between structure, morphology, and ultimate performance of nanostructured hybrid materials in electrical and electro-optical applications. To this end activities are planned to (1) develop new organic and polymeric materials enabling performant nanostructured hybrid materials, (2) study morphology, electronic structure, optical and electronic properties, electrical transport mechanisms and charge or energy transfer mechanisms of the hybrid materials obtained and (3) incorporate these materials in innovating photovoltaic concepts and explore additional generic valorisation possibilities. It is also within the objectives of the project to develop materials which are compatible with environmentally friendly solvents for processing and thin film technology, suitable for large-scale production.

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    Systematic investigation of the mechanisms for efficient 3-photon absorption and fluorescence in organic molecules. 01/10/2003 - 30/09/2004

    Abstract

    Hyper-Rayleigh scattering measurements are being performed, using a picosecond amplified lasersystem with a new efficient setup with gated parallel detection. With this system it is possible to perform hyper-Rayleigh scattering measurements at a whole range of wavelengths, to determine the dispersion of the first hyperpolarisability of organic molecules. Thanks to the high sensitivity of the setup it is also possible to measure third-order hyper-Rayleigh scattering for the determination of the second hyperpolarisability of organic molecules. In addition, the non-linear optical processes 3-photon absorption and fluorescence (3PF) will be examined. Therefore instrumental developments are necessary, in order to determine the 3PF-efficiencies and their dependence on the excitation wavelength.

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    Excitons and polarons in low bandgap polymers : optical generation and charge carrier separation. 01/10/2003 - 30/09/2004

    Abstract

    In this Ph.D-project research will be done on the characterisation of the properties of polymers with applications in plastic electronics, photovoltaic cells, organic light-emitting diodes and organic semi-conductors. In particular the characterisation of the photo-excited states (singlet and triplet states), the study of polarons and the study of the charge separation process, of vital importance in photovoltaics. The following techniques will be used; optical absorption and fluorescence spectroscopy, (L)EPR-spectroscopy ((Light induced) Electron Paramagnetic Resonance) and ODMR-spectroscopy (Optical Detected Magnetic Resonance) in X-band (~9.5GHz) as well as in W-band (~95GHz).

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    Structure analysis of paramagnetic metallocenters in proteins by pulse EPR and ENDOR at X- and W-band microwave frequencies (9.5 and 95 GHz). 01/01/2003 - 31/12/2007

    Abstract

    Using continuous wave (CW) and pulse electron paramagnetic resonance (EPR) and the related electron nuclear double resonance (ENDOR) and electron double resonance (ELDOR) techniques different paramagnetic metalloproteins and paramagnetic centers in solids will be investigated. The study is mainly focused on the structural analysis of the iron-containing heme group in different globins and on the investigation of the nickel enzyme methyl-coenzyme M reductase and its model systems. In both cases the structural information can give direct access to the analysis of the different proposed biological functions of the proteins under study. In a broader framework, the above-mentioned techniques will be applied in the analysis of transition metal ions in photo-refractive materials and in catalytic systems. Furthermore, new EPR and ENDOR pulse sequencies will be developed aimed at improving spectral resolution and interpretation.

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    Supramolecular Functional Systems: Interaction of Molecular Components with Microcrystalline Semiconductors. 01/01/2003 - 31/12/2004

    Abstract

    Recent imaging systems based on silver halide or AgX technology use combinations of spectral sensitisers (organic molecules) to increase the sensitivity. When two different sensitisers are brought together on one surface new processes occur. In order to further optimise the sensitivity more information about the interaction between the different molecules on the surface is needed. In this study the influence of the interaction on the electron hole processes will be studied by a number of optical and magnetic resonance techniques. The EPR-spectrum is a characteristic for the paramagnetic radicals that are formed during illumination of the sample. Differences in the energy levels caused by the interaction between the molecules will give rise to different optical absorption spectra and growth and decay kinetics of the radicals.

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    Multi-wavelength nonlinear optical spectroscopy of organic materials. 01/10/2002 - 30/09/2005

    Abstract

    Organic and organometallic materials for non-linear optical (NLO) applications are investigated by non-linear and time-resolved laser spectroscopy. Molecular hyperpolarisabilities are determined, e.g. by hyper-Rayleigh scattering at variable laser wavelength with fluorescence correction through spectral analysis. Based on the experimental results, and in close collaboration with several synthesis groups, new NLO materials are developed. Also materials for two-photon absorption and two-photon induced fluorescence applications are developed.

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    Structure determination of paramagnetic centers in solids and in molecular compounds by means of high frequency (95GHz) and pulsed EPR and ENDOR spectroscopy. 01/01/2002 - 31/12/2005

    Abstract

    In this project we wish to study by means of pulsed W?band EPR- and ENDOR-spectroscopy, the electronic structure of paramagnetic centers in a series of solids and molecular compounds which could not be previously investigated. W-band EPR is needed because of different reasons: insufficient resolution of the EPR-spectrum at lower frequencies, high zero-field splittings for which a minimal energy quantum is needed, or very small dimensions of the available single crystals for which a higher absolute sensitivity is a important. Pulsed or FT EPR yield information about the spin relaxation times, which is a first step to obtain selective measurements of EPR spectra via Elektronen-Spin-Echo-(ESE)-detection. An important part however is the precise determination of hyperfine interactions between the electrons and nuclei in the the center which can be obtained either by Electron Spin Echo Envelope Modulation (ESEEM) or by means of Pulsed ENDOR. (Implementation of pulsed W-band ENDOR has been submitted but not yet been accepted in this project).

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    Modern EPR spectroscopy-methodology and applications in physics, chemistry and biology. (Conference project) 01/01/2002 - 31/12/2004

    Abstract

    Electron Paramagnetic Resonance (EPR) spectroscopy has witnessed during the last 15 years tremendous methodological and instrumental developments primarily in the directions of high field EPR and pulsed EPR. These include multi-frequency, multi- resonance and multi-dimensional experiments, analogous to the earlier developments in NMR spectroscopy. These advances increase considerably the information content extracted from EPR measurements and has therefore impacted various areas of chemistry, materials, physics and biology. The objectives of the school is to disseminate modern EPR methodology to the scientific community through its young researchers. It will effectively expose young scientists to the newest developments in EPR spectroscopy along with novel research applications, and it will give them the theoretical tools essential for the comprehension of the various techniques.

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    Characterization of high-spin transition metal compounds by means of sophisticated EPR-techniques at high microwave frequency. 01/01/2002 - 31/12/2003

    Abstract

    By means of high frequency (95GHz) EPR-techniques specific families of organo metallic compounds can be studied. These systems have a high groundstate spin and can behave as single molecule magnets. The key to such behaviour is the zero-field splitting of the energy levels (=splitting of the energy levels in the abscence of a magnetic field). These zero-field splittings can be precisely analyzed using high frequent EPR techniques.

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    Allowance for research equipment : pulsed X-band EPR and ENDOR spectrometer. 01/01/2002 - 31/12/2002

    Abstract

    Paramagnetic species such as radicals, transition metal ions and conduction electrons can be investigated with Electron Paramagnetic Resonance (EPR) and Electron Nuclear Double Resonance (ENDOR). The magnetic properties, the local symmetry and the structure of the centers can be determined as well as the coupling with nearby electronic or nuclear spins. The pulsed technique is particularly powerful for time-resolved studies (spin relaxation) and for the detection of spin correlations.

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      Photoluminescence spectroscopy from anti-Stokes laser excitation of the excited electronic state of the optical 3H center in diamond. 01/01/2002 - 31/05/2002

      Abstract

      This project is concerned with a specific defect in diamond, the so-called 3H center, which is produced by electron irradiation and involves a self-interstitial. The goals of the research are: 1-An investigation of the temperature dependence of the photoluminescence (PL) intensity of the 3H-center under anti-Stokes laser excitation (at 514.5 nm). For this purpose we will study the influence of the excitation energy using excitation by a tunable dye laser. 2-We will investigate the gradual transfer of intensity in the 503.6 nm line of the 3H centre towards a new line at 507.6 nm, attributed to a new defect. Both PL and Electron Spin Resonance (ESR) will be employed for further identification of the defects.

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        Scientific mission (sabbatical) FWO . 01/06/2001 - 30/09/2001

        Abstract

        During this scientific mission in the laboratory of Prof. D. Gatteschi, Florence, Italy, I wish to concentrate on the following important aspects of the research of molecular magnetic materials: 1-The application and interpretation of macroscopic measurements for magnetic charaterization. 2-High-frequency EPR-measurements in the range up to 360 GHz with the new spectrometer at the university of Pisa, built in a consortium with the guest laboratory of this mission in Florence. 3-The theoretical methods to describe the magnetic properties of these compounds in terms of the molecular structure.

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          Nonlinear light scattering and multiphoton absorption in molecular optical materials. 01/01/2001 - 31/12/2006

          Abstract

          The 2nd and 3rd order nonlinear optical (NLO) properties of organic and organometallic compounds will be investigated by means of advanced spectroscopic techniques, in particular elastic and inelastic nonlinear light scattering 'hyper-Rayleigh (at the 2nd and 3rd harmonic) en hyper-Raman scattering' and also multiphoton absorption spectroscopy. To this end, a high-performance apparatus will be constructed based on a novel laser system with kilohertz repetition rate and a multi-channel detector for parallel measurement of the spectra.

          Researcher(s)

          Research team(s)

          Supramolecular Functional Systems: Interaction of Molecular Components with Microcrystalline Semiconductors. 01/01/2001 - 31/12/2002

          Abstract

          Recent imaging systems based on silver halide or AgX technology use combinations of spectral sensitisers (organic molecules) to increase the sensitivity. When two different sensitisers are brought together on one surface new processes occur. In order to further optimise the sensitivity more information about the interaction between the different molecules on the surface is needed. In this study the influence of the interaction on the electron hole processes will be studied by a number of optical and magnetic resonance techniques. The EPR-spectrum is a characteristic for the paramagnetic radicals that are formed during illumination of the sample. Differences in the energy levels caused by the interaction between the molecules will give rise to different optical absorption spectra and growth and decay kinetics of the radicals.

          Researcher(s)

          Research team(s)

            Defects in diamond-like materials of the B/C/N system. 11/12/2000 - 11/12/2003

            Abstract

            Diamond and cubic boron nitride (cBN), as materials with very similar structure, exhibit, remarkable structural and electronic properties. Due to their extreme hardness both materials are the choice superabrasives in machine tooling operations. As wide gap semiconductors, diamond and especially cBN are very promising materials, in the form of thin films, for a future generation of high- temperature, high-pressure and radiation-resistant fast microelectronic devices, optoelectronic applications and field effect devices. Despite the crucial influence of the lattice defects (intrinsic or impurity type) on the physical and materials related properties, the defect characterization of these materials, especially as crystalline films, has begun only recently to receive a more systematic attention. In addition, nowadays diamond and cBN can be both p- and n-type doped, but the current results are still very far from the expectation as concerns the carrier mobility, doping reproducibility and understanding how dopants are incorporated. This concerns specially the n-type diamond and p- type cBN. In addition the preparation of cBN in the form of thin films is still a technological endeavor. For electronic applications, even the hexagonal BN is a very wide gap interesting material of which the main properties are unknown.

            Researcher(s)

            Research team(s)

            Laser spectroscopy of ultrafast relaxation and transport phenomena in complex material systems. 01/10/2000 - 30/09/2008

            Abstract

            Ultrafast and nonlinear laser spectroscopies are applied to the investigation of the properties of epitaxially grown semiconductor structures and of organic compounds for photonic applications. Also hybrid systems, consisting of organic films on semiconductor substrates, will be studied.

            Researcher(s)

            Research team(s)

            Investigation of the potential energy conversion efficiency of organic solar cells based on donor/acceptor heterojunctions. 01/10/1999 - 30/09/2001

            Abstract

            Recently efficient charge separation and conduction was demonstrated in mixtures of organic materials, e.g. C60/poly-(arylene-vinylene) mixtures. In the initial phase the opto-electronic properties of such films will be characterised and optimised. A set-up for controlled production of the films by vapor deposition will be constructed. Structural, as well as electrical and optical characterisation methods will be employed. Finally, electrode layers will be deposited to obtain operational solar cells, and their efficiency will be further investigated.

            Researcher(s)

            Research team(s)

              Optical and opto-electronic technologies and design techniques for VLSI-Photonics. 31/03/1999 - 31/03/2001

              Abstract

              This programme of basic generic research is a collaboration with groups of the Universities of Brussels and Ghent (VUB and RUG) and with the Inter-University Micro-Electronics Center (IMEC). In this framework the laboratories of the University of Antwerp (UA) are contributing to the search for new light source materials. In particular, we pursue optimalisation of structure of the arylene-vinylene oligomers and polymers for this application in order to obtain blue Organic LEDs with improved lifetime, efficiency and color purity.

              Researcher(s)

              Research team(s)

                Multidisciplinary spectroscopic research of organic materials and biomolecules. 01/01/1999 - 31/12/2002

                Abstract

                In the proposed concerted action fundamental properties of synthetic organic compounds and biomolecules will be studied, giving emphasis to the study of their molecular and electronic structure with the aid of the following spectroscopic methods: electron spin resonance (ESR), mass spectrometry (MS), nuclear magnetic resonance (NMR) and vibration spectroscopy (IR-absorption and Raman diffraction). The research team includes four laboratories with state-of-the-art instrumentation and internationally recognized expertise with regard to the above mentioned spectroscopic methods, and two associated laboratories which are active in a complementary way in the preparation and evaluation of the materials studied. The research will focus on two classes of materials: (i) Biomolecules, more specifically, carbohydrate, lipid-like and polyphenolic compounds. These biomolecules show in general a high natural complexity with regard to their structure as well as their function. They show a broad range of biological activities, have already resulted in useful pharmaceuticals and are still important in the development of the latter. Some of these biomolecules enjoy a current interest with regard to prevention against degenerative diseases and cancer. (ii) Aromatic oligomers and polymers with electrical and optical applications. Some technologically relevant examples are conducting polymers, - with chemical detectors as a specific application -, and polymeric light-emitting diodes (LED's). In the synthesis of these materials a large variation of compounds can be prepared and in some cases structure determination of the molecules is desirable. In addition, the determination and engineering of electronic and other functional properties is important for the applicability of the materials.

                Researcher(s)

                Research team(s)

                  Paramagnetic centres in solids: applications and microscopic characterisation by EPR and ENDOR techniques. 01/12/1997 - 10/03/2001

                  Abstract

                  Paramagnetic centres will be investigated in a series of materials, such as tooth enamel, irradiated sugars, and zeolithes. In each of these compounds there is a direct connection with applications in the medical, food and chemical sector. The microscopic structure of the centres will be studied by means of Electron Paramagnetic Resonance (EPR) and when needed, high-resolution techniques such as Electron-Nuclear Double Resonance (ENDOR) and High Frequency (HF) EPR will be applied. The latter measurements can be performed in the HFEPR instrument which is operational in the Antwerp laboratory in the framework of a recent FWO-project.

                  Researcher(s)

                  Research team(s)

                    Investigation of the potential energy conversion efficiency of organic solar cells based on donor/acceptor heterojunctions. 01/10/1997 - 30/09/1999

                    Abstract

                    Recently efficient charge separation and conduction was demonstrated in mixtures of organic materials, e.g. C60/poly-(arylene-vinylene) mixtures. In the initial phase the opto-electronic properties of such films will be characterised and optimised. A set-up for controlled production of the films by vapor deposition will be constructed. Structural, as well as electrical and optical characterisation methods will be employed. Finally, electrode layers will be deposited to obtain operational solar cells, and their efficiency will be further investigated.

                    Researcher(s)

                    Research team(s)

                      Dynamical breakdown of micrometer AlGaAs/GaAs tunneling structures under DC load and under ultrafast electrical pulses. 01/10/1997 - 31/03/1998

                      Abstract

                      In this project we plan to combine the techniques for ultrafast detection of electrical currents, developped at the Semiconductor Physics Institute (SPI) in Vilnius, with the possibilities for picosecond laser experiments in the Laboratory for Experimental Solid State and Laser Physics (EVSL, UIA), in order to investigate the contributions to electrical breakdown of III/V semiconductor tunneling structures.

                      Researcher(s)

                      Research team(s)

                        Probing the structure of quantum mechanics : new probability models for new experiments on quantum particles. 20/12/1996 - 19/06/2000

                        Abstract

                        An intensive collaboration between theoreticians working on the structures of quantum mechanics and experimentalists, is at the heart of this project. The three main themes are : (i) the phenomenon of light radiation by a single delocalised atom, (ii) experimental tests of the hidden variable models developped by the Brussels group and (iii) the problem of the (non) classical nature of the quantum probability.

                        Researcher(s)

                        Research team(s)

                          Laser spectroscopy of ultrafast relaxation and transport phenomena in complex material systems. 01/10/1996 - 30/09/2000

                          Abstract

                          Ultrafast and nonlinear laser spectroscopies are applied to the investigation of the properties of epitaxially grown semiconductor structures and of organic compounds for photonic applications. Also hybrid systems, consisting of organic films on semiconductor substrates, will be studied.

                          Researcher(s)

                          Research team(s)

                            Characterization and optimisation of metal-organic charge-transfer compounds for applications in photonics. 01/07/1996 - 30/06/1998

                            Abstract

                            All-optical signal processing will become on the medium term an important technology in telecommunications and information processing. We can make an significant contribution to optimise the required photonic materials, together with three foreign groups which are synthesising original molecular compounds and work on their characterisation and application in devices. In our laboratory the EFISHG, HRS, and QEO characterisation techniques as well as ultrafast laser spectroscopy are available for this. The group of organic synthesis in our university will also provide doped polymer films for this project.

                            Researcher(s)

                            Research team(s)

                              Ultrafast switching and relaxation processes in III/V heterostructures and devices. 01/01/1996 - 31/12/2001

                              Abstract

                              Ultrafast opto-electronic response of AlAs/GaAs heterostructure devices i.e. resonant tunneling light-emitting diodes (RTLED) and related devices, will be investigated by picosecond measurements of the electroluminescence. Moreover, high-sensitivity photoluminescence spectra will be studied in structures related to the quantum-cascade laser in order to learn about optimal condition for population inversion in the electronic subbands.

                              Researcher(s)

                              Research team(s)

                                Optically and Electrically Detected High-Frequency (lOOGHz) Electron Spin resonance in Condensed Matter. 01/01/1996 - 31/12/2001

                                Abstract

                                A high frequency (HF) Electron Spin Resonance (ESR) spectrometer will be installed and optical and electrical detection of magnetic resonance will be implemented in order to conduct a fundamental research program on a series of condensed matter systems of great interest. These include dye radicals at the surface of silver halide microcrystals, radicals in photochemical reactions, optically active oligomers in polymeric light-emitting diodes, deep and shallow electron traps in semiconductors, and nanostructures. Also, systems with small g-anisotropy, or with large zero-field splitting can be investigated. HFESR yields a high absolute sensitivity which permits the investigation of very small samples.

                                Researcher(s)

                                Research team(s)

                                  ESR and optical study of loss-mechanisms for the radiative recombination in polymeric light-emitting diodes. 01/10/1995 - 30/06/1996

                                  Abstract

                                  The efficiency of future light-emitting diodes (LED) based on polymeric materials is fundamentally limited by unwanted recombination processes in the films and at interfaces. In this project we plan to characterise these processes by electrically and optically detected Electron-spin-resonance (ESR) and by ultrafast time-resolved laserspectroscopy. Different types of polymeric materials (e.g, oligomer/polymer-blends or copolymer based) will be compared. This research is meant to contribute to the optimisation of these polymeric devices.

                                  Researcher(s)

                                  Research team(s)

                                    Investigation of relaxation and transport processes in epitaxially grown semiconductor structures by means of ultrafast optical measuring techniques. 01/01/1995 - 31/12/1996

                                    Abstract

                                    Exciton relaxation processes in AlGaAs/GaAs multiple quantum wells and minority-carrier transport in AlAs/GaAs resonant tunneling structures are investigated with down to femtosecond time resolution. Optical excitation and probing is performed in the visible and near infrared by mode-locked and/or amplified laser sources.

                                    Researcher(s)

                                    Research team(s)

                                      Femtosecond time resolved linear and non linear spectroscopies in the near infrared and ultravilet. 01/01/1995 - 31/12/1995

                                      Abstract

                                      With intense femto- and picosecond laser pulses ultra fast phenomena are studied in condensed matter : rotons and vibrons in molecular crystals (H2,N2), radiationless relaxation of optically excited defects in ionic crystals, ultra fast transport and luminiscence processes in semiconductor heterostructures and non linear optical properties of pi-conjugated polymer molecules.

                                      Researcher(s)

                                      Research team(s)

                                        Laser spectroscopy of ultrafast relaxation and transport phenomena in complex material systems. 01/10/1994 - 30/09/1996

                                        Abstract

                                        Ultrafast and nonlinear laser spectroscopies are applied to the investigation of the properties of epitaxially grown semiconductor structures and of organic compounds for photonic applications. Also hybrid systems, consisting of organic films on semiconductor substrates, will be studied.

                                        Researcher(s)

                                        Research team(s)

                                          Optical memory effects in thin organic films on epitaxially-grown semiconductor structure. 01/10/1993 - 31/12/1994

                                          Abstract

                                          Charge transfer between dye molecules in an organic film and a III/V semiconductor substrate are being studied with ultrafast optical measuring techniques, with special interest in the resulting memory effects. The speed of charge transfer and its reversal, as well as the dependence on the substrate properties is under investigation.

                                          Researcher(s)

                                          Research team(s)

                                            Femtosecond time-resolved linear and non-linear laserspectroscopies in the near infrared and ultra-violet. 01/01/1993 - 31/12/1994

                                            Abstract

                                            Study of ultra-fast electronic, vibrational, rotational and optical processes in solids using linear and non-linear femtosecond laserspectroscopies, specifically molecular crystals, semiconductors, conducting polymers and defects in ionic materials.

                                            Researcher(s)

                                            Research team(s)

                                              Femtosecond near-infrared spectroscopy; additional optical components. 01/01/1993 - 31/12/1993

                                              Abstract

                                              Specific optical components are being acquired for ultrafast laser spectroscopy, in the near-infrared region, on semiconductor and organic materials with large optical nonlinearities. This requires components with low dispersion and wavefront distorsion.

                                              Researcher(s)

                                              Research team(s)

                                                Impulsive stimulated light scattering from vibrational and rotational excitations in solids 01/10/1992 - 30/09/1994

                                                Abstract

                                                Impulsive excitation with femtosecond laser pulses enables us to investigate low-frequency Raman-active vibrational and rotational transitions. This technique, implemented in either a high frequency (82 Mhz) unamplified, or a low frequency (2kHz) amplified laser system, will be applied to the study of complex molecular crystals (e.g. naphtalene)

                                                Researcher(s)

                                                Research team(s)

                                                  Picosecond electro-optic response of bipolar resonant tunneling structures. 01/06/1992 - 31/12/1995

                                                  Abstract

                                                  The response of AlAs/GaAs resonant-tunneling light-emitting diodes (RTLED's) upon excitation by picosecond light and electrical pulses is investigated. The generation of electrical pulses by means of the RTLED's will be applied in a stand-alone system (60 ps resolution) for the characterization of fast switching devices.

                                                  Researcher(s)

                                                  Research team(s)

                                                    Investigation of relaxation and transport processes in epitaxially grown semiconductor structures by means of ultrafast optical techniques 01/01/1991 - 31/12/1994

                                                    Abstract

                                                    Two-dimensional exciton relaxation is investigated in III-V semiconductor heterostructures by time-resolved reflectivity, transparancy and photo-luminescence measurements. In a series of AlAs/GaAs resonant tunneling structures, with two or three barriers, and with n-or p-doped contact layers, our interest focuses on tunneling of minority-electrons and -holes, and on fast electro-optic switching.

                                                    Researcher(s)

                                                    Research team(s)

                                                      Impulsive stimulated inelastic light scattering of vibrational ì and rotational excitations in solidsì 01/10/1990 - 30/09/1992

                                                      Abstract

                                                      Impulsive stimulated light scattering will be applied to investigate the femtosecond relaxation of low-frequency vibrations and rotations in molecular crystals, and of lattice vibrations in different solid-state systemen. To this end, fiber pulse compressions (down to 60 fs) is combined with laser-pulse amplification at high repetition frequencies (up to 2 kHZ)

                                                      Researcher(s)

                                                      Research team(s)

                                                        Study of femto second dynamics with ultra-short amplified laserpulses. 01/10/1986 - 30/09/1994

                                                        Abstract

                                                        Study of ultra-fast electronic-, vibrational- and rotational processes in solids using non-linear pico- and femtosecond time-resolved laser spectroscopies, in particular molecular crystals and defects in solids.

                                                        Researcher(s)

                                                        Research team(s)